Catalytic reactions between hydrocarbons and steam are strongly endothermic. Several types of reforming processes have been developed through the years, each having unique features. The tubular reformer has eventually become preferred as tube metallurgy has progressed. Tubular reformers, which are directly fired have evolved with operating pressures ranging from atmospheric to 600 PSIG or more and the tube metal temperatures of up to 1800.degree. F. or higher. In the early years of steam-hydrocarbon reforming, many users equated performance with the life of the catalyst as manifested by catalyst strength. This was due to the fact that the vast majority of reforming furnaces were designed so conservatively that virtually any reforming catalyst would demonstrate satisfactory performance so long as the catalyst remained physically intact. However, some of the more modern high-severity reformers are much less conservative in design. As a result localized catalyst activity becomes the limiting feature of the catalyst as high activity must be maintained to maintain tube temperatures within allowable limits.
New catalyst in a commercial reformer reaches lined out performance immediately after startup regardless of the catalyst type used. Within a rather wide range initial activity can be affected by specific nickel surface area, nickel form and particle size. Lined out catalyst activity is not appreciably affected by nickel concentrations above approximately 30 percent, or nickel crystaline sizes below about 200 A or overall catalyst surface area. The effective nickel concentration or metallic concentration in the range of from 6 to 30 percent is about the effective range above which additional catalytic metal on the carrier does not produce any appreciable result.
Catalyst particle size or geometric surface area does have a marked influence on activity exhibited under all operating conditions. One reason attributed to the increase in activity is attributed to the improved heat transfer characteristics obtained as well as the increased superficial or geometric catalytic surface exposed which significantly increases gas diffusion rates to catalytic sites. The improvement which can be obtained in activity by going to smaller catalyst sizes is significant. This approach has been very successful in overcoming localized activity problems encountered in operating units. It has been widely accepted therefore, all other factors being equal, that the catalytic efficiency of a particular catalyst for the steam-hydrocarbon reforming reaction, is directly proportional to the geometric surface area of the catalyst pellet. It would be expected that a catalyst pellet containing a plurality of axially disposed gas passages and having a large superficial geometric surface area because of the interior walls of the gas passages would exhibit proportionally higher catalyst efficiency for the steam-hydrocarbon reaction. Applicants found however that the expected increases in catalytic efficiency did not occur with catalyst tablets containing a plurality of gas passages. Applicants therefore concluded that the catalytic efficiency provided by the geometric surface area of the exterior surface of the catalyst tablet was not achieved with the geometric surface area of the interior walls of the gas passage of said catalyst tablet.